Magnetic apparatus for laterally converging the beams of a triple gun cathode ray tube



May 12, 1970 A. M. ANTHONY 3,512,023

. MAGNETIC APPARATUS FOR LATERALLY CONVERGING THE BEAMS OF A TRIPLE GUN CATHODE RAY TUBE Filed April 16, 1969 lNjZS/TOR Glberi 7 izom M ali ys' United States Patent US. Cl. 31377 9 Claims ABSTRACT OF THE DISCLOSURE To adjust the lateral convergence of the first electron beam relative to the second and third beams, five magnets are disposed side by side along a line transverse to the axes of the beams. The fields of the magnets are transverse to such line, and also to the axes. The third magnet is opposite the first beam. The polarization of the second and fourth magnets is opposite to that of the other magnets. Moreover, the fields of the second and fourth magnets are sufficiently stronger than the fields of the other magnets to predominate in the regions around the second and third beams, while the field of the third magnet predominates in the region around the first beam. Thus, the magnets displace the first beam in one lateral direction while displacing the second and third beams in the opposite lateral direction. The magnets displace the beams along the x-axis while neutralizing any tendency towards displacement along the y-axis. Preferably, the magnetsare incorporated into a single magnetic memher which is rod shaped and rotatably adjustable about its own axis.

This invention relates to an apparatus for laterally converging the three electron beams of a triple gun cathode ray tube, which may be of any known or suitable type adapted to be employed in a color television system.

The need for such lateral convergence is recognized in the'art relating to color television picture tubes, and various arrangements have been provided by the prior art, as attempts to meet this need. The general purpose of the lateral convergence apparatus is to displace one electron beam laterally, relative to the other two beams. Conventionally, the blue beam of the color television picture tube is displaced along the x-axis relative to th red and green beams.

'In one aspect the present invention is an improvement upon the lateral convergence apparatus disclosed in FIGS. 6 and 7 of the U.S. patent to Rennick, No. 3,308,328, issued Mar. 7, 1967. The Rennick convergence apparatus utilizes five magnets disposed side by side and preferably combined into a single rod shaped magnetic member mounted opposite the neck of the cathode ray tube. The third magnet is opposite one of the beams, usually the blue beam. The magnets are spaced along a line transverse to the axes of the beams, and the fields of the magnets are transverse to such line, and also to the axes of the beams. The polarization of the second and fourth magnets is opposite to that of the first, third and fifth magnets.

3,512,023 Patented May 12, 1970 The five magnets of the Rennick arrangement produce displacement of the blue beam along the x-axis, while substantially neutralizing any tendency towards displacement of the red and green beams along the y-axis. Moreover, there is no displacement of the blue bea-m along the yaxis.

The Rennick arrangement has the disadvantage that the displacement of the blue beam along the x-axis is accompanied by a smaller displacement of the red and green beams in the same direction along the )x-axis. This displacement of the red and green beams in the same direction as the blue beam makes it more diificult to achieve lateral convergence.

The principal object of the present invention is to provide an improved arrangement whereby the red and green beams are displaced along the x-axis in a direction opposite to the displacement of the blue beam. This arrangement makes it much easier to attain the lateral convergence of the beams.

In accordance with the present invention, the five magnet arrangement of the Rennick patent is modified and improved by giving the second and fourth magnets substantially greater field strength than the third magnet. Moreover, the second and fourth magnets are also preferably stronger than the first and fifth magnets. The mag netic fields of the second and fourth magnets are sufficiently stronger than the fields of the other magnets to predominate in the regions of the red and green beams, while the field of the third magnet predominates in the region of the blue beam. With this improved arrangement, the lateral displacement of the blue beam in one direction along the x-axis is accompanied by lateral displacement of the red and green beams in the opposite direction along the x-axis. Thus, the relative displacement is greater, so that the desired lateral convergence is more easily achieved. The magnets effectively neutralize any tendency towards displacement of the beams along the y-axis.

Further objects, advantages and features of the present invention will appear from the following description taken with the accompanying drawings, in which:

FIG. 1 is a diagrammatic cross section showing the lateral convergence apparatus to be described as an embodiment of the present invention.

FIG. 2 is a cross sectional view showing additional details of the lateral convergence apparatus.

FIG. 3 is a typical graph showing the field strengths of the five magnets employed in the lateral convergence apparatus.

As just indicated, FIGS. 1 and 2 illustrate a lateral convergence apparatus 10 adapted to be employed in connection with a triple beam cathode ray tube 12, which may be of the type commonly employed in color television systems. In the illustrated tube 12, the three beams are designated B for blue, R for red and G for green. The beams are generated by three electron guns 14B, 14R and 14G, disposed in a triangular or delta arrangement, as clearly shown in FIG. 2. The electron guns are suitably supported, as by means of three saddle shaped brackets 16 having their ends secured to insulating supports 18. Electron guns 14B, R and G are disposed within the neck portion 20 of the cathode ray tube 12.

To achieve lateral convergence of the three electron beams B, R and G, the apparatus 10 utilizes five magnets 2125 disposed side by side, opposite the neck of the cathode ray tube 12. The magnets 21-25 are arranged along a line extending transversely to the axes of the electron beams B, R and G. It will be seen that the third magnet 23 is opposite one beam, usually the blue beam B. The other magnets 21, 22, 24 and 25 are outboard relative to the third magnet 23.

Preferably,.the five magnets 21-25 are incorporated into a single magnetic member 26, with five pairs of magnetic poles to produce the five magnets. The illustrated magnetic member 26 is in the form of a generally cylindrical rod which is rotatably adjustable about its own axis, so that the effective strength of all the magnets can be changed simultaneously.

As shown in FIG. 2, the rod shaped magnetic member 26 is mounted for rotary adjustment in a holder 28 which is suitably secured to the neck 20 of the tube 12, as by means of a spring 30. The holder 28 has a bore 32 in which the rod 26 is rotatably adjustable. It is preferred to provide a spring 34 in the holder 28 for frictionally retaining the rod 26. The spring 34 insures that the rod 26 will remain in any adjusted position.

The north and south poles of the magnets 21-25 are indicated by the letters N and S in FIG. 1. It will be seen that the poles of each magnet are on diametrically opposite sides of the magnetic member or rod 26. The sec ond and fourth magnets 22 and 24 are polarized oppositely, relative to the first, third and fifth magnets 21, 23 and 25. Thus, the polarity of the magnets alternates along the sequence of five magnets.

In accordance with the present invention, the strength of the second and fourth magnets 22 and 24 is substantially greater than that of the third magnet 23. Moreover, the second and fourth magnets 22 and 24 are preferably greater strength than the first and fifth magnets 21 and 25.

The third magnet 23 is relatively close to the first electron beam B. Thus, the field of the third magnet 23 predominates in the region of the beam B.

Because of the greater strength of the second and fourth magnets 22 and 24, the fie ds of these magnets are sufiiciently strong to predominate in the regions of the second and third beams R and G, respectively.

The field of the third magnet 23 causes displacement of the first beam B in one direction along the x-axis, as indicated by the vector 43 in FIG. 1. Because of the reverse polarity of the second and fourth magnets 22 and 24, the second and third beams R and G are displaced in the opposite direction along the x-axis as indicated by the vectors 42 and 44. The opposite displacement of the red and green beams, relative to that of the blue beam, makes it easier to achieve the desired convergence.

The arrangement of the five magnets 21-25 is such that there is virtually no displacement of the beams B, R and G along the y-axis. This is illustrated by the magnetic field map which has been superimposed upon FIG. 1. Several lines of force are shown, with appropriate arrows to indicate the direction of the magnetic field. Three boundary lines 52, 53 and 54 are shown along which the y-component H of the magnetic field is zero. The blue beam B is directly on the boundary line 53, while the red and green beams R and G are virtually on'the boundary lines 52 and 54. These boundary lines 52, 53 and 54 extend downwardly from the poles of the magnets 22, 23 and 24.

FIG. 1 also shows boundary lines 56 and 57 along which the x-component H of the magnetic field is zero. The polarity of the x-component changes when these bounlary lines are crossed. It will be observed that the red beam R is on the opposite side of the boundary line 56 from the blue beam B. Similarly, the green beam G is on the opposite side of the boundary line 57 from the blue beam B. i

The graph of FIG. 3 represents the field strength of the five magnets 21-25. It will be seen that the graph has five peaks 61-65 corresponding to the five magnets 21-25. The second and fourth peaks 62 and 64 are substantially higher than the third peak 63, thus indicating the greater strength of the second and fourth magnets 22 and 24. The second and fourth peaks 62 and are also higher than thefirst and fifth peaks 61 and 65, so as to'indicate that the second and fourth magnets 22 and 24 are stronger than the first and fifth magnets. Preferably, the third magnet is also appreciab y stronger than the first and fifth magnets, as indicated by the greater height of the third peak 63. f

The lateral displacement of the blue beam B is adjusted by' rotating the magnetic member or rod 26 about its own axis in the holder 28, This adjustment changes the effective field strength of all five magnets 2125. The blue beam is displaced in one direction along the x-axis, as indicated by the vector 43 in FIG. 1. The red and green beams R and G are displaced in the opposite direction along the x-axis, as indicated by the vectors 42 and 44. This opposite displacement results from the greater strength of the second'and fourth magnets 22 I and 24 so that the fields of these magnets predominate in the regions around the red and green beams R and G. There is no appreciable displacement of the beams along the y-axis.

The opposite lateral displacement of the red and green beams R and G, relative to the displacement of the blue beam B, is highly advantageous, because the desired convergence of the beams is achieved more easily and with a weaker effective magnetic field. 'It is significantly easier to adjust the beams to the desired convergence with the apparatus of the present invention.

I claim:

1. A lateral convergence apparatus for a cathode ray tube having a triangular arrangement of three electron guns for developing three electron beams,

said apparatus comprising an array of five magnets disposed side by side along a line extending transversely to the axes of'the electron'guns,

said magnets having fields transverse to said line and also to said axes,

the third of said magnets being centrally disposed opposite one of said beams produced by one of said guns,

the second and fourth of said magnets being polarized oppositely relative to the other magnets, said second and fourth magnets having substantially greater field strength than said third magnet whereby said magnets produce displacement of said one electron beam in one lateral direction while displacing the second and third electron beams in the opposite lateral direction. 2. Apparatus according to claim 1,, in which the second and fourth magnets have substantially greater field strength than the first and fifth magnets. 3. Apparatus according to claim 1, in which the first, third and fifth magnets have approximately equal field strength. i

4. Apparatus according to claim 1,

in which said five magnets are incorporated into a single magnetic member extending along said line,

said magnetic member having five pairsof magnetic poles to form said five magnets. a

5. Apparatus according to claim4, in which said member is in the form of a generally cylindrical rod, Y the five pairs of poles being spaced along said rod," the poles of eachpair being diametrically opposite each other. i I

6. Apparatus according to claim 5,

including means holding said rodfor rotary adjustment about its own'axis to change the effectivetfield strength of "all said'niagnets simultaneously.

7. Apparatus according to claim 5, the field of the third magnet being predominant in the in which the second and fourth magnets have subregion around the first beam.

stantially greater field strength than the first and fifth magnets, as well as the third magnet. References Cited 8. Apparatus according to claim 1,

. 5 UNITED STATES PATENTS 1n WhlCh the fields of said second and fourth magnets are sufiiciently stronger than the field of said third 3308328 3/1967 Rennick 313' 77 magnet to predominate in the regions around said second and third electron beams. JAMES W. LAWRENCE, Primary Examiner 9. Apparatus according to claim 1, 10 V. LAFRANCHI, Assistant Examiner in which the magnetic fields of said second and fourth magnets are sufiiciently stronger than the fields of US C X.R.

the other magnets to predominate in the regions around the second and third electron beams, 

